Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 270239
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
839 PM MDT WED AUG 26 2015

.DISCUSSION...

ONLY MINOR ADJUSTMENTS TO GRIDS THIS EVENING. WHAT LITTLE
THUNDERSTORM ACTIVITY THAT DEVELOPED THIS AFTERNOON HAS
DECREASED. HOWEVER, ECHOES ARE STARTING TO SPREAD BACK INTO
BEAVERHEAD COUNTY, SIMILAR TO THE FORECAST MODELS INDICATED. HAVE
THEREFORE KEPT MENTION OF STORMS ACROSS SOUTHWEST MONTANA AND
ADDED MENTION OF GUSTY WINDS, AS EARLIER STORMS HAD GUSTS IN
EXCESS OF 30 MPH. OTHERWISE, WINDS AND TEMPERATURES ARE ON TRACK.
COULSTON

&&

.AVIATION...
UPDATED 0010Z.

WIDESPREAD LOW VFR/HIGH MVFR CONDITIONS WITH SOME MOUNTAIN
OBSCURATION ARE EXPECTED AT LEAST THROUGH THURSDAY DUE TO ONGOING
WILDFIRES. MONSOONAL MOISTURE WILL ALSO INCREASE DURING THE
PERIOD, SPREADING MID/HIGH LEVEL CLOUDINESS NORTHEAST ACROSS THE
AREA. A FEW THUNDERSTORMS WILL MOVE OVER SOUTHWEST MONTANA THROUGH
06Z, BUT THE LIKELIHOOD IS LOW THAT THEY WILL DIRECTLY IMPACT THE
KBZN TERMINAL AREA. HOWEVER, BRIEF WIND GUSTS TO 30 KT ARE
POSSIBLE THERE DUE TO PASSING THUNDERSTORMS. THE AIRMASS WILL
DESTABILIZE AGAIN AFTER 16Z AND A WEAK SURFACE FRONTAL BOUNDARY
WILL MOVE INTO THE AREA, WHICH MAY CAUSE ISOLATED TO SCATTERED
THUNDERSTORMS TO DEVELOP, MAINLY SOUTH OF A KCTB-KHVR LINE. AGAIN,
GUSTY WINDS WILL BE THE MAIN THREAT, BUT SOME STORMS MAY PRODUCE
BRIEF HEAVY RAIN. WINDS WILL ALSO SHIFT MORE WESTERLY BEHIND THE
BOUNDARY AND BECOME GUSTY ALONG THE EAST SLOPES OF THE ROCKIES.
COULSTON

&&

.FIRE WEATHER...

WARM AND DRY CONDITIONS PERSIST OVERNIGHT WITH LIGHT WINDS AND
MODERATE TO POOR MIDSLOPE HUMIDITY RECOVERY. A WEAK DISTURBANCE
WILL WEAKEN THE UPPER LEVEL RIDGE ON THURSDAY WITH INCREASING
MONSOONAL MOISTURE. A LEE TROUGH ASSOCIATED WITH THIS WAVE WILL
STRENGTHEN THE SURFACE PRESSURE GRADIENT. MODEL CROSS SECTIONS
INDICATE A WEAK MOUNTAIN WAVE SIGNATURE. HENCE EXPECT SURFACE
WINDS TO TURN WESTERLY AND STRENGTHEN THURSDAY AFTERNOON ALONG
THE ROCKY MOUNTAIN FRONT AND ADJACENT PLAINS...WHILE AFTERNOON
HUMIDITY DROPS INTO THE TEENS. CRITICAL FIRE WEATHER CONDITIONS
ARE POSSIBLE IN THIS AREA. FURTHER SOUTH...A MIX OF WET AND DRY
THUNDERSTORMS ARE EXPECTED OVER THE CENTRAL MONTANA DISTRICTS
THURSDAY AFTERNOON AND EVENING. PW VALUES CLIMB WELL ABOVE
AVERAGE TO AROUND 0.8 INCHES. THIS ACTIVITY MAY PRODUCE FREQUENT
LIGHTNING...BUT CONFIDENCE REMAINS LOW ON COVERAGE AND RAINFALL
AMOUNTS. SPC DAY 2 OUTLOOK HIGHLIGHTS SCT DRY THUNDERSTORMS OVER
CRITICALLY DRY FUELS. WILL CONTINUE TO MONITOR FOR POSSIBLE FIRE
WEATHER HIGHLIGHTS. A DRY COLD FRONT WILL MOVE INTO THE AREA
SATURDAY BRINGING GUSTY WINDS...LOW RH VALUES AND NEAR CRITICAL
FIRE WEATHER CONDITIONS THIS WEEKEND. NUTTER

&&

.PREV DISCUSSION...
/ISSUED 610 PM MDT WED AUG 26 2015/

TONIGHT THROUGH FRIDAY...HOT AND DRY CONDITIONS CONTINUE AS A
BROAD THERMAL TROUGH REMAINS IN PLACE BENEATH AN UPPER LEVEL
RIDGE OF HIGH PRESSURE. A WEAK UPPER LEVEL TROUGH PRECEDED BY A
PUSH OF MONSOONAL MOISTURE IS MOVING ACROSS UTAH INTO WESTERN
WYOMING. SCATTERED SHOWERS AND THUNDERSTORMS WILL DEVELOP LATE
THIS AFTERNOON AND EVENING AS THE TROUGH MOVES BY THE REGION.
THIS ACTIVITY WILL BE SHORT LIVED AND PRODUCE VERY LITTLE
PRECIPITATION. WILDFIRE SMOKE CONTINUES TO PRODUCE UNHEALTHY AIR
QUALITY AND REDUCE VISIBILITY BELOW 6 MILES IN MANY AREAS. THE AIR
QUALITY ALERT ISSUED BY THE MT DEQ REMAINS IN EFFECT UNTIL FURTHER
NOTICE. A SMALL UPPER LEVEL WAVE EJECTS FROM THE DEEP LOW TO OUR
WEST AND FLATTENS THE RIDGE OVER MONTANA THURSDAY. MODEL CROSS
SECTIONS INDICATE A POTENTIAL FOR DOWNSLOPE WINDS TO BECOME
ENHANCED WITH DEEP MIXING OVER OUR NORTHWEST COUNTIES THURSDAY
AFTERNOON. HAVE RAISED WINDS SLIGHTLY ABOVE GUIDANCE AND ISSUED A
FIRE WEATHER WATCH ALONG THE ROCKY MOUNTAIN FRONT AND ADJACENT
PLAINS DUE TO WINDS AND LOW HUMIDITY. SEE THE FIRE WX DISCUSSION
BELOW FOR MORE DETAILS. WIDESPREAD SHOWERS AND THUNDERSTORMS ARE
ALSO POSSIBLE OVER CENTRAL AND SOUTHWEST MONTANA THURSDAY
AFTERNOON. PW VALUES EXCEEDING 0.75 INCHES INDICATE A MIX OF WET
AND DRY THUNDERSTORMS WITH THE POTENTIAL FOR FREQUENT LIGHTNING.
WARM AND DRY CONDITIONS ARE EXPECTED FRIDAY WITH STRONG WESTERLY
WINDS ALOFT AND LIMITED MOISTURE AVAILABILITY. NUTTER

FRIDAY NIGHT THROUGH WEDNESDAY...HAVE NOT MADE ANY SIGNIFICANT
CHANGES TO THE GOING FORECAST. MODELS CONTINUE TO KEEP AN UPPER
LEVEL TROUGH OVER THE GULF OF ALASKA AND RIDGING OVER THE HIGH
PLAINS THROUGH MUCH OF THE PERIOD. THIS PATTERN WILL KEEP
SOUTHWEST FLOW ALOFT OVER MONTANA WITH NO MAJOR STORMS OR HEAT
WAVES EXPECTED DURING THE MEDIUM RANGE. BIGGEST DIFFERENCE THAT
SHOWS UP BETWEEN THE TWO MODELS IS THAT THE GFS EJECTS ENERGY
OVER THE PACIFIC NORTHWEST DURING THE WEEKEND THEN MOVES IT INTO
MONTANA ON MONDAY FOR MORE WIDESPREAD POPS. HOWEVER, THE ECMWF
KEEPS THE BULK OF UPPER LEVEL ENERGY IN WESTERN CANADA AND
REMAINS GENERALLY DRY. PREVIOUS FORECAST PACKAGE AND WPC
SOLUTIONS FAVORED THE ECMWF SOLUTION THAT KEEPS ISOLATED POPS AND
SEASONABLE TEMPERATURES IN PLACE FROM MONDAY THROUGH WEDNESDAY SO
WILL KEEP WITH THIS SOLUTION FOR NOW. MPJ

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  59  91  59  89 /   0  20  10  10
CTB  52  88  53  86 /   0  10  10  10
HLN  55  90  53  89 /  10  30  20  10
BZN  54  86  49  87 /  10  40  20  10
WEY  40  76  38  79 /  20  50  30  10
DLN  52  84  48  86 /  10  30  20  10
HVR  55  92  56  89 /   0  10  10  10
LWT  59  87  57  87 /   0  30  20  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
FIRE WEATHER WATCH FROM THURSDAY AFTERNOON THROUGH THURSDAY
EVENING FOR MTZ112-114.

&&

$$

WEATHER.GOV/GREATFALLS


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